Drill strings of pipe for oil and gas wells are assembled or disassembled vertically on a derrick one joint at a time, and are stored horizontally on pipe racks situated on the ground adjacent the rig. The work floor of the rig is typically elevated substantially above the pipe rack such that transferring sections of pipe to and from the racks and the work floor is necessary, and further requires careful handling of the heavy pipe to protect the workers and the pipe.
Conventional systems based on a boom having a pipe receiving trough in which pipe may be placed typically also include some way to assist with moving heavy sections of pipe along and out of such trough.
A variety of pipe cars, skates, bumpers, conveyors, stops and other devices (e.g. U.S. Pat. No. 4,371,302) have been described to control the motion of sections of pipe between a rig and ground.
For example, the applicant's Canadian application CA 2224638 relies on a spring loaded bumper mounted on the proximal end of a telescoping rod to push sections of pipe along the trough as well as to absorb the impact of pipe sliding down the trough toward the distal end thereof.
U.S. Pat. No. 6,533,519 to Tolmon (‘519’) issued 18 Mar. 2003 teaches a carriage member separate from a pusher member, both driven on a single axis aligned with the center of a pipe receiving groove. Disadvantageously, '519 and similar “ram based” designs that push a carriage member up the center of a trough require heavy, bulky hydraulic cylinders that are often restricted along the trough they can move a carriage, and further have limited response times such that the average speed of the carriage is low, causing pipe handling operations to take significant time.
U.S. Pat. No. 3,143,221 to Blacken (‘221’) issued 4 Aug. 1964 teaches a pipe car pulled and released by a cable, having 2 sets of side-mounted wheels each set having a common axle, the wheels running in a channel in a fixed track. Importantly, the track along which the pipe car is designed to roll is stationary and does not move vertically or longitudinally like the boom of most modern pipe handling systems. Disadvantageously, this wheeled pipe car design and other similar pipe car designs that are pulled by a single cable along a center line, although capable of running substantially the full length of the boom, are unstable and the wheels and axles tend to wear prematurely with the wheels binding in their guide tracks. A further disadvantage of the discrete wheel & track based design is that the coupling of the pipe car to the pipe handling system takes place at only four discrete points on the tracks, at any given moment. Very significantly the stability of the 221 design is problematic when the track in which the wheeled pipe car rides must move between the ground and work floor levels such that a reinforced track and a braking assembly become necessary. No pipe car design incorporating such features and which provides a relatively inexpensive addition to a raiseable pipe-handling apparatus is known.
The prior art in the oil field services industry has concentrated on teaching variations on center-line pushing devices covering only a portion of the boom length. Designs based on pipe cars having discrete wheels situated in tracks provide a limited coupling of the pipe carrying device (“car”) to a relatively fragile set of members, resulting in a design that is less reliable, less stable and less safe than might be achieved using similar components. Moreover, none of the prior art reviewed teaches a device that is driven in both directions on both sides, failing to address the risk of runaway pipe cars.
Accordingly, there exists a real need for a pipe handling apparatus which provides such features as braking and ability to propel a pipe car in two mutually opposite directions, so as to improve modern pipe handling apparatus.